CONDENSED CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Income Statement [Abstract]
OPERATING REVENUES	$ 944,955	$ 783,531
OPERATING EXPENSES
Fuel and purchased power	394,504	265,269
Operations and maintenance	250,080	218,342
Depreciation and amortization	191,906	186,605
Taxes other than income taxes	57,138	57,998
Other expenses	610	825
Total	894,238	729,039
OPERATING INCOME	50,717	54,492
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	15,061	9,747
Pension and other postretirement non-service credits - net (Note 5)	9,865	23,809
Other income (Note 9)	6,077	1,704
Other expense (Note 9)	(4,131)	(3,422)
Total	26,872	31,838
INTEREST EXPENSE
Interest charges	88,119	65,389
Allowance for borrowed funds used during construction	(12,722)	(4,482)
Total	75,397	60,907
INCOME BEFORE INCOME TAXES	2,192	25,423
INCOME TAXES	1,183	4,161
NET INCOME	1,009	21,262
Less: Comprehensive income attributable to noncontrolling interests	4,306	4,306
NET INCOME (LOSS) ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ (3,297)	$ 16,956
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING — BASIC (in shares)	113,358	113,102
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING — DILUTED (in shares)	113,358	113,295
EARNINGS PER WEIGHTED-AVERAGE COMMON SHARE OUTSTANDING
Net income (loss) attributable to common shareholders - basic (in dollars per share)	$ (0.03)	$ 0.15
Net income (loss) attributable to common shareholders — diluted (in dollars per share)	$ (0.03)	$ 0.15